Chapter 10Sedimentary Rocks
Sedimentary Rocks
Accumulations of various types of sediments
Compaction: pressure from overlying sediments squeezes out air and water
Cementation: dissolved minerals in water form a “glue” that holds sediments together
Sedimentary Rocks
Classified by…Kind of sediments
Size of sediments
that form them
Clastic Sedimentary Rocks
Rock fragments carried by wind, water, ice and deposited
Classified by size
Clastic
Conglomerate: Rounded gravel fragments or pebbles
Clastic
Conglomerate wall
Clastic
Breccia:Angular gravel fragments with sharp corners
Clastic
Breccia wall
Clastic
Sandstone:Sand-sized grains
Mostly quartz
Pore spaces- allow groundwater and oil to flow
Clastic
ShaleClay-sized particles
Cemented and compacted under pressure
Flat, flaky layers
Chemical Sedimentary RocksMinerals dissolved in water, settle out with change in temperature
Ex. Limestone when calcite settles out of ocean water
Evaporites: dissolved minerals left over when water evaporates; turns to rock
Chemical
Ex: Gypsum, halite
Ex: Great Salt Lake, UT
Organic Sedimentary Rocks
Organic: formed from the remains of living things
Ex: coal
Organic
LimestoneShell build up on ocean floor, from
• Clams
• Oysters
• Plankton
Ex: chalk
Organic
White Cliffs of Dover, England
Sedimentary Rock Features
Easily identifiable
Include:Stratification (layering)
Ripple marks
Mud cracks
Fossils
Concretions
Stratification
Change in type of sediment deposited
Layers!!
Vary in thickness
Stratification
Cross bedding
Stratification
Graded bedding: where in the layer do you think the largest and heaviest grains of sediment settle?
Ripple Marks
Formed by action of wind or water on sand
Preserved when sand sandstone
Mud Cracks
Formed when muddy deposits dry and shrink
River plains, dry lake bed
New deposits fill in
Fossils
Remains or traces of ancient plants and animals
Buried as sediments build up
Hardest parts sometimes remain, but often dissolve into rock
Concretions
Lumps, or nodules, of rock with composition different from main rock body
Minerals precipitated from solutions build up around rock particles
Concretions
Groundwater deposits quartz, calcite
Geodes
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